[luatex] "Proper" use of \Udelimiterover &c

[Manuel Pégourié-Gonnard]

Hi Taco, hi Will,

Le 14/07/2010 09:34, Will Robertson a écrit :
> On 14/07/2010, at 4:53 PM, Taco Hoekwater wrote:
>> When I implemented this, I did not realise that this would make sense.
>> Is such a construct as this *always* a large operator?
> 
> Well, the idea is that you either use the overbrace "naked" and it doesn't
> matter about the operator stuff, or you give it an attached piece of math as
> in this example.
> 
> So the Plain definition of \overbrace is
> 
> \mathop{\vbox{[...snip!...]}}\limits
> 
> so that you can place material directly on top.
> 
> As for your question, I think the answer is, therefore, "yes".
> 
I'm not sure I agree. Your argument about Plain's definition of \overbrace is
very convincing, but does it cover all uses of \Udelimiterover? Or are macros
such as \overrightarrow or "generalized \widehat" likely to be reimplemented
using \Udelimiterover too?

If the answer to the second question is yes, then I think it would be safer to
leave things as they are and continue to handle the \mathop{...}\limits part at
the macro level when it is needed (the new primitive would "only" replace the
\ialign{...} part in the current definition of \overbrace IIUC).

Manuel.